var stream = require("stream");

var Readable = stream.Readable;

function MyReadable(){
    Readable.call(this);
    var c = 'a'.charCodeAt(0);
    this._read = function(){
        console.log(c);
        if(c < 'z'.charCodeAt(0)){
            this.push(String.fromCharCode(c++));
        }else{
            this.push(null);
        }
    }
}

var myReadable = new MyReadable();
myReadable.pipe(process.stdout);